Color television systems



July 19, 1955 cs. c szIKLAl 2,713,606

COLOR TELEVISION SYSTEMS Filed April 18, 1952 a sheets-sheet 1 INVENTORk l j' Cm July 19, 1955 G. c. szlKLAl 2,713,606 COLOR TELEVISION SYSTEMSFiled April le, 1952 z sheets-sheet 2 F0605 CWZ M ,72% Lf 4W 5/.Pf'/7A/5F/ 7/ Z/ y i INVENTOR ATTORNEY Zfllib Patented duly 19, 1955 ticertf/rasee cf een retevision srsrntus George C. Sziitlai, Princeton, N.i., assigner to Radio Corporation or' America, a corporation of lelawareApplication April l, 1952, Serial No. 282,979 9 Claims. (Cl. 17d-5.4)

This invention relates to color television methods, and moreparticularly it providing reproduction of color in subcarrier systems.

it is desirable to provide a color television system in which the entiresignal information, that is,

and saturation signal components, directly and efficiently by differentelements producing device to produce a color picture. systems haveheretofore been proposed, such ample, the one shown and described in myU. S. application, Serial No. 165,031, filed May 29, 1950, entitledVisual indicating Systems. ln the system referred to immediately above,a phase modulation component of the signal, which represents hue, isused to direct or desysterns and relates to apparatus for phasemodulated color is utilized of the re- Some such as, for exphasemodulated subcarrier is additionally utilized for changing the beam sizeor focus so that the desired numberof colorreproducing elements arebombarded by the beam. In this manner the proper combinations of colorsare selected to provide the desired hue and saturation, and thebrightness component is provided by intensity modulating the beam toproduce directly in the kinescope a color picture from the incomingvideo information.

Certain registration and efficiency problems are pro vided in colortelevision systems utilizing kinescopes having a plurality of electronbeam guns. lin the system above described, it is possible to utilize asingle gun color reproducing device since all information other than thebrightness component is applied to deiection and focussing electrodes inthe kinescope.

Therefore, cathode ray tubes may be constructed without the reject costdue to used in color television systems, and also to increase the lightefliciency of the tube. Accordingly, a ruled line screen single guncathode ray tube is preferred in nccordance with the present invention.

.ln using colored line screens on cathode ray tubes with adjacentlypositioned horizontally oriented ruled colored lines having differentselected component light producing elements, for example, red, green andblue, it has been a problem to accurately direct the beam to the desiredcolor line combination. This is generally true because commerciallyfeasible circuits for dciiecting the cathode ray beam do not accuratelyfollow a straight color line entirely across the face of the kinescope.Accordingly, elaborate registration schemes have been developed.Examples of these registration systems may be found n my U` S. PatentNo. 2,587,074, 26, i952, entitled Color Television Image lic-producingSystem, and the U. S. Patent L11-90,8 l2, dated December 13, 1949,issued to C. E. Huffman, entitled Control for Color Television. Furtherregistration systems have been the brightf copending provided for threegun ruled line color tubes such as the copending U. S. application,Serial No. 198,213, flied by entitled Color Television Registration 9:'erred to immediately above, circuitry has been provided for solving theregistry problem.

ln accordance with the` present invention, however, both colorreproduction and color registration are accurately provided by a In thismanner, improved circuit efciency is made possible with a simple andreliable reproducing tube structure, and the reproduced picture on thescreen is caused to comply not only with changes in signal informationbut t0 correct for error information creeping into the system at anypoint.

It is therefore an object of the present invention to light producingelements.

It is a further object of this invention to provide an with televisionand amplitude modulated with color saturation information.

Another object of the invention is to provide an improved televisionsystem in which and saturation information is utilized directly bydilferent to provide a Figure the present invention;

Figure 3 is a graphical representation of potentials derived from thesignal which are useful in obtaining beam focussing;

Figure 4 is a block diagram of a circuit embodiment for obtaining focuscontrol potentials in accordance with the invention; and

Figure 5 is a circuit of the invention.

Throughout the drawing, like reference characters will be used toindicate like circuit elements in order to facilitate comparison. Thosecircuits whose details may not of themselves be a part of the presentinvention are shown in block diagram form in order that the nature ofthe invention might more readily be ascertained.

In Figure 1 any suitable television receiver It) is provided fordetecting a video signal for use in the video :impliier 12 and having acolor subcarrier component whose diagram of a further embodimentinvolved may be found, for

carrier reference frequency 1S on the back porch of the horizontal syncpedestal. The burst l5 may be separated from the video by burst gatecircuits 16 to phase control a reference signal oscillator i8 therebymaintaining it in an accurate phase relationship with the subcarriergenerator at the transmitter.

The usual deiection and high voltage circuits 20 are provided forcausing the electron beam generated in the kinescope 22 to scan theruled color lines which form the kinescope screen. The amplitude of thevideo wave represents the brightness component of the picture and isused to intensity modulate the the cathode ray beam by application tothe control element 23. There is contained in the video brightnesssignal the subcarrier component whose phase and amplitude represent thecolor hue, and saturation information, respectively. Accordingly, on thekinescope screen, there will be developed a modulation component at thesubcarrier frequency which may, the video response characteristic of thesystem, say 3.99 megacycles. The subcarrier is chosen to have afrequency so related to the scanning frequency that a minimum ofinterference occurs between the color information and the brightnessinformation.

A plurality of separate sampling devices such as the photo-electriccells 28, 29 and 30 with the corresponding red, blue and green passfilters are used to detect the subcarrier at the reproduction level.This information is suitably amplied and filtered by apparatus 28a, 29a,and 30a, if necessary to comprise a signal voltage Es correspondinglyinserted at one input terminal of the respective red, blue, and greenphase comparator circuits 31, 32 and 33. The subcarrier phase may bedetected by comparing it with a reference signal Er derived from thecolor subcarrier oscillator 1S in the respective phases 95 Q52, (a, in amanner similar to that practiced in current color subcarrier systems. Bychoosing the proper polarity and phase, output potentials will beobtained from the phase comparator circuits with such as to providedeflection anrd focus potentials to the kinescope beam by means of theauxiliary deflecting and focusing electrodes 35 and 36. These electrodesmaybe constructed by those skilled in the art to have such configurationand location to deect the beam and focus it in accordance withpotentials developed at the respective common output terminals and 41 ofthe several phase comparator circuits. A teaching of the principles thusexample, in publications such as the textbook Fernsehen by Dr. F.Schrter, published in Berlin by Julius Springer in 1937, which containsa chapter on Electron Optic Geometry containing the principles involvedin the construction of focussing and deflecting lens configurations.

Consider now that a color signal is reproduced on only the biue colorlines of the kinescope. The subcarrier signal component will be pickedup at only photocell 29 and inserted at the blue phase comparatorcircuit 32 along with the reference potential of phase e2. Assuming forthe moment that the subcarrier signal is occupying a zero relative phaseangle indicating proper color hue reproduction for blue, the referencesignal qta will be chosen at a phase-angle in order to provide betweenthe phase comparator output terminals 40 and 41 a balanced or Zerodeection potential output condition. Thus, if the color subcarrier phaseindicates blue is the desired color and blue is the only color obtainedat the sampling cells, there will be no deflection of the beam. The sameoperation holds true for the red and green subcarrier components ineffecting deilection. The respective phase angles assumed to identifythe color components may be changed with a corresponding change of thereference signal phase used for comparison. For purposes of readycomparison a table is provided for red, green, and blue for example, bea frequency near the upper end of l sense and amplitude in 'i ycolorsaturation is less hue color signals and two sets of correspondingreference signal phase conditions as follows:

B G R 4 Zero output at 0 120D 240 Reference signal phase.. 90 210 330Zero output at 0 197 90 Reference signal phase.. 90 287 180 Should thecolor information not fall upon the proper ruled line, the balancecondition will not exist (except when no signal potential is present)and a properly sensed deecting potential will be developed between theterminals 40 and 41 by current or electron ilow coming from the outputterminals of one or a plurality of the phase comparator circuits in thedirection indicated by the arrows above the output resistors 44 and 45.

Considering in detail this phase of operation, assume that thesubcarrier falling on the blue lines has a relative phase of indicatingthat the color hue green should be reproduced. The phase comparators 3land 33 for the red and green signals will have no input signal potentialand therefore will provide no output deection potential. The blue phasecomparator 352, however, will develop a potential corresponding to thephase difference between the signal developed and the reference signalat phase qg. Accordingly, deilection potentials are developed in outputresistors 44e and 4S to provide a potential differential betweendeflection electrodes 35 and 36 of enough magnitude to deflect the beamfrom the blue line to the green line. At this time, a balance or nullcondition is reached in both the blue and green phase comparators 32 and33, thereby providing no deflection potential and maintaining the beamin registration on the green line. Like action is provided whether oneor a plurality of signals is present since the output signal of eachphase comparator circuit is used to deiiect the beam. lt is noted thatin a standard television system, the deflection angle provided by theauxiliary electrodes 35 and 36 is small, being in the order of 1/525 ofthe total vertical deflection angle, and therefore reliable colorregistration is readily obtained.

The foregoing analysis was made with the assumption that the beam wouldbe focussed on a single line. Assume now that the beam impinges on aspot which should represent only a blue subcarrier component but whichis so large that it overlaps onto both the red and green lines. Ashereinbefore mentioned, the color subcarrier amplitude denotes colorsaturation. Since only blue information is present the saturation ismaximum and the subcarrier would have maximum amplitude. The phasecomparator circuits are therefore so chosen that they lare responsive toamplitude in the following manner. When a signal voltage is obtainedbalanced current components ilow in both resistors 44 and 45 so that nodifferential potential is established between the deliecting electrodes35 and 36, but the average potential as compared with surroundingelectrodes is changed thereby affecting the focus of the beam.

Figure 2 illustrates schematically a phase comparator circuit whichoperates in this manner. As the signal potential Es is applied, bothdiodes 50 and 51 conduct upon opposite alternations of the signalpotential to cause a balanced current flow in the resistors 44 and 45.The greater the signal amplitude, the greater the potential developed atthe terminals 40 and 41 as compared with vthe midtap terminal 53 or theinput terminal Eb at which a biasing or auxiliary focussing potentialmay be added. lt is therefore apparent that any subcarrier signalcomponent ES present on the kinescope screen will cause the beam to befocussed to a smaller vertical area depending upon the amplitude of thesubcarrier.

When the subcarrier amplitude is not at a maximum the and a white signalmight be mixed with the color signal to obtain the present reproduction.Thus, me beam will be slightly defocused (in the vertical direction)supplying a white component made up of a portion of rect, blue, andgreen light so that automatic saturation control is obtained by changingthe beam focus. When the subcarrier amplitude is zero, the beam coversall the red, green, and blue lines so that a monochrome signal isreproduced.

Such a relationship of potential on the focusing elec trodes as comparedwith vertical beam width is shown in Figure 3 where the potential is thesummation of the rectified signal and reference potentials with thebiasing potential as expressed by the term It(Es}-L`r)-l-Eb. Theparabolic curve is shown to indicate that phase relationship between thesignal and reference potentials may be either leading or lagging toeffect the desired automatic focus operation.

lf a phase comparator is desired which is nonresponi sive to subcarrieramplitude variations in the manner described, or should a separatedeiiecting and focusing system be desired, the circuit of Figure 4 maybe used in accordance with the invention to obtain focus controlpotential. Thus, the block et? indicates any suitable source of colorsubcarrier along with the side bands which may be found, for example, inthe video circuits of a television receiver. The color subcarrier isthen amplitude detected at the block circuit dll and filtered at theblock circuit 62 to provide the desired focus control potential at theoutput lead Eb. This potential, as that above described, is of anamplitude variable with the color saturation information, and may beconnected at terminal S3 of Figure to supplement or provide focuscontrol, as desired.

Although the system described is more stable when a separate phasecomparator is utilized for each primary color reproduced by the tube,satisfactory operation may be obtained with the simplified system ofFigure 5. In this system, the sampling means are shown as conductiveelements ati/ted to the green and blue lines on the kinescope screen. ltis thereby recognized of course that color sampling may be accomplishedby any other desired means and is not limited to the specificembodiments shown.

Different phase comparison circuits are shown here than those abovedescribed. In order to simplify eX- apart. it is to be recognized thatthe invention may be adapted by those skilled in the art to apply orderreversal systems and the like, simplicity and to enable a more readygrasp of the principles of the present invention, these features are notconsidered.

In the embodiment of Figure 5, and 7l are utilized for the purpose ofobtaining a higher signal potential at the transformers 72 and i3 aswell the insertion of a gain control component having an amplitudeobtained as a function ot the overall brightness of the signal from lead74. The purpose f this feature is to permit high chroma colorsindependent of the brightness or beam intensity, and is more completelydisclosed in the cepending U. S. application of A. V. Bedford, SerialNo. 130,204, tiled November 20, 1949.

Phase comparison is made in the additional pentode tubes 75 to 78 whichare amplitude responsive and in The output detiecting potentials of thesystem at terminals 40 and 41 will be dependent upon the relative phasesof the signals in the same manner as the phase comparator Clt willprovide a focusing potential dependent upon the amplitude of thecarmeans sampling a plurality ot' individual colors reprophasecomparator circuits duction and color registration is accuratelyprovided.

2. A system as defined in claim l wherein said deflection means compriseeiectrodes so placed and constructed to afford beam focusing and thepotentials derived at such phase comparator circuits automatically causebeam focusing upon a desired number of color lines when said beam ismodulated by said signal sub-carrier component indicating the presenceof color.

3. A system of automatic focus control for directing the beam of acolored line-screeii cathode ray tube to one or a plurality of linewidths comprising in combination, means sampling color signals of aseparate primary suba phase comparator circuit, means moduwhereby bothcolor reproand a carrier source and said sampling means to said phasecomparator circuit in such trol potential automatically determining beamwidth whereby for color signals a small spot is formed on said screenand for monochrome signals a large spot is formed on said screenencompassing a plurality of said colored lines thereby apparentlyresolving the lines into a monochrome picture.

4. A system as defined in claim 3 wherein deiiecting means is providedfor said tube connected to phase recomprising in combinaa colorsubcarrier phase indicates color hue, deiiecting upon desired colors,means having two input circuits and means sampling color signals ofseparate colors produced by said elements coupled to one of said inputcircuits, a color subcarrier reference signal connected to the other ofsaid input circuits, and a circuit connecting said output circuit tosaid deiiecting amasar;

7 means whereby color signals are automatically registered for providingthe hue indicated by the color subcarrier phase.

6. A system as defined in claim 5 having focusing means for said beam,and a circuit connecting said output circuit to said focusing means forautomatically determining the beam width as a function of the colorsubcarrier amplitude component.

7. In a system for receiving color television signals including a colorsubcarrier wave component whose phase indicates hue and whose amplitudeindicates saturation and for reproducing an image from said signals upona ruled line, single beam color image-reproducing means, the combinationincluding: means responsive to said color television signals formodulating the intensity of said beam, whereby the light produced bysaid imagereproducing means is modulated at subcarrier wave frequencyand phase; means for sampling the modulated light from saidimage-reproducing means; a source of a color subcarrier referencesignal; means coupled to said light sampling means and to said referencesignal source to develop a signal representative of a color other thanthat indicated by the phase of said color subcarrier wave; and beamdeflection means operable in response to said developed colorrepresentative signal to direct said beam to one of said ruled linesproducing the color indicated by the phase of said color subcarrierwave.

8. In a system for receiving color television signals including a colorsubcarrier wave component Whose phase indicates hue and whose amplitudeindicates saturation and for reproducing an image from said signals upona color image-reproducing means, the combination including: meansresponsive to said color televison signals for modulating the intensityof said beam, whereby the light produced by said image-reproducing meansis modulated at subcarrier wave frequency and phase; means for samplingthe modulated light from said imagereproducing means; a source of acolor subcarrier reference signal; phase comparator means coupled tosaid phase comparator light sampling means and to said reference signalsource to develop a signal representative of a color other than thanthat indicated by the phase of said color subcarrier wave; and beamdeflection means operable in response to said developed colorrepresentative signal to direct said beam to the color indicated by thephase of said color subcarrier wave.

9. In a system for receiving color television signals including a colorsubcarrier wave component whose phase indicates hue and whose amplitudeindicates saturation and for reproducing an image from said signals upona color image-reproducing means, the combination including: meansresponsive to said color television signals for modulating the intensityof said beam, whereby the light produced by said image-reproducing meansis modulated at subcarrier wave frequency and phase; means for samplingthe modulated light from said image-reproducing means; a source of acolor subcarrier reference signal; phase comparator means coupled tosaid light sampling means and to said reference signal source to developa signal representative of a color other than that indicated by thephase of said color subcarrier wave; beam deflection means operable inresponse to said developed color representative signal to direct saidbeam to the color indicated by the phase of said color subcarrier wave;and means responsive to the amplitude of said color subcarrier wave forchanging the spot size of said beam.

References Cited in the tile of this patent UNITED STATES PATENTS2,415,059 Zworykin Jan. 28, 1947 2,490,812 Huffman Dec. 13, 19492,530,431 Huffman Nov. 21, 1950 2,545,325 Weimer Mar. 13, 1951 2,568,543Goldsmith Sept. 18, 1951 2,635,140 Dome Apr. 14, 1953 2,657,257 LestiOct. 27, 1953

